1. Field of the Invention
The present invention relates to a duplexer module in which a monitoring element used to monitor a transmission output is connected to a duplexer provided on a multilayer substrate or a printed substrate.
2. Description of the Related Art
For a front-end portion of a cellular phone or the like, a duplexer is adopted that performs conversion between a reception signal and a transmission signal and antenna common signals. In recent years, as duplexers, discrete components have been adopted, each of which includes an integrated combination of a transmission filter, a reception filter, and a phase adjustment circuit, and the duplexer thereof is mounted on a substrate, thereby configuring a duplexer module. In some cases, in the duplexer module, a coupler is inserted into an antenna common line connected to an antenna common terminal of the duplexer, and a portion of the electrical power of a transmission signal is transmitted to a monitoring line, thereby monitoring a transmission output (for example, refer to Japanese Unexamined Patent Application Publication No. 09-270619).
In the above-mentioned duplexer module, owing to the insertion loss of the coupler inserted into the antenna common line, the receiving sensitivity of a reception signal is deteriorated. In addition, the isolation of the monitoring line for a reception line is deteriorated, and isolation between a transmission line and the reception line is also deteriorated. Accordingly, it may be considered that a coupler is inserted into the transmission line connected to a transmission signal terminal of the duplexer. However, in that case, an influence such as the insertion loss of the duplexer itself or the like is not included in a signal detected in the coupler at that position, and it is difficult to correctly monitor the transmission signal.